The present invention relates to a respiration flowmeter, which makes use of ultrasonic waves.
Recently, there has been recognized the necessity of monitoring a respiration function of a patient, inter alia a postoperative serious case. To effect this, it is essential to continuously monitor a flow velocity or flow rate of the respiration, as its basic approach. A first and important requirement for the inspiration flowmeter used for such end is not to inflict a physical and mental load on the patient. Particularly, the respiration flowmeter structured to give a difficulty in breathing, is improper. Conventional flowmeters such as differential-pressure type flowmeters, hot-wire type flowmeters or turbine type flowmeters have been used as respiration flowmeters, but, in measuring the respiration at a low flow velocity of a newborn, for example, the respiration flowmeters of these types work unstably or more adversely cannot measure the respiration flow rate. Generally, on the other hand, when comparing the expiration with the inspiration, there are great differences in temperature, humidity and gas composition. Therefore, even in case of the respiration flowmeter using the ultrasonic wave, a measuring error arising from a change of an ultrasonic propagating velocity in the respiration gas under measurement is not negligible. Thus, the conventional respiration flowmeters have been unsuccessful in providing perfect solutions to the above problems.